The invention relates generally to optical parametric oscillators and particularly to laser systems comprising optical parametric oscillators.
Wavelength tunable laser systems are frequently constructed with optical parametric oscillators. Optical parametric oscillators are commonly constructed with a crystal having nonlinear optical properties disposed between two mirrors, referred to as an optical cavity. Referring generally to FIG. 1, an optical parametric oscillator can include an optical cavity 10 comprising two parallel plane mirrors 20a and 20b, whose surfaces are treated to be reflective or transmissive, based on the wavelength of incident light. A nonlinear crystal 30 is disposed between mirrors 20a and 20b. In operation, a laser beam 40, referred to as the pump or pumping laser beam, passes through the back of first mirror 20a and into nonlinear crystal 30. Nonlinear crystal 30 converts laser beam 40 into two coherent waves of a signal frequency (fs) and a complementary or idler frequency (fi), such that the frequency (fp) of pump laser beam 40 is equal to the signal frequency plus the idler frequency (fp=fs+fi)
Simple optical parametric oscillators can be constructed so that the inner facing surfaces of mirrors 20a and 20b are treated to reflect the signal beam. The inner surface of first mirror 20a is generally treated to reflect the idler beam. However, the inner surface of second mirror 20b is generally treated to transmit the idler beam outside of the optical cavity. Alternatively, optical parametric oscillators can be constructed in a xe2x80x9cdoubly resonant configurationxe2x80x9d, in which the mirrors are treated to reflect one of the beams (i.e., the signal beam) completely and second mirror 20b is constructed to transmit one of the beams (i.e., the idler beam) only partially and to reflect a portion of the idler beam back into the crystal. This xe2x80x9cdoubly resonantxe2x80x9d configuration permits the use of pump beams with a lower intensity, while still achieving sufficient optical activity by the nonlinear crystal and transmitting an appropriate wave from the optical cavity.
When an appropriate crystal 30 with appropriate birefringence properties is selected, the frequency of the beam emitted by the OPO can be tuned by adjusting the orientation of the optical axis (crystalline axis) of crystal 30 with respect to the optical axis of the OPO. In alternative embodiments, two or more nonlinear crystals can be used in place of single crystal 30.
Optical parametric oscillators can have drawbacks. For example, the longwave tuning range of existing OPOs has generally been limited to the 4 to 5 xcexcm range. This is not suitable for many scientific applications.
Accordingly, it is desirable to provide a laser system including an optical parametric oscillator which can emit beams that are widely and easily tunable within desired frequency bands and are of a relatively low power. It is also desirable to provide a laser system including an optical parametric oscillator which overcomes other drawbacks and deficiencies of the prior art.
Generally speaking, in accordance with the invention, an optical parametric oscillator and a laser system including an optical parametric oscillator, is provided for producing widely tunable coherent light over about 6 xcexcm, such as in the range of at least about 7.5 xcexcm to 16 xcexcm and even about the 7 to 18 xcexcm range. Optical parametric oscillators in accordance with the invention advantageously include CdGeAs2 (CGA) crystals. When grown properly, such crystals, in accordance with the invention, can exhibit exceptionally small ( less than 0.1 cmxe2x88x921) losses in intensity. Laser systems in accordance with the invention can include CO2 lasers as the pump beam and frequency doublers or changers, such as CGA crystals.
Accordingly, it is an object of the invention to provide improved optical parametric oscillators.
Another object of the invention is to provide improved wavelength tunable laser systems.
Another object of the invention is to provide an improved method of making an optical parametric oscillator and laser system.
The invention accordingly comprises the features of construction, combinations of elements, and the arrangements of parts and the steps for effecting the foregoing, and the scope of the invention will be indicated in the claims.